We live in a world surrounded with computers. Not just personal computers but also computers embedded in electronic devices, appliances, cars, toys, mobile phones, etc. Every computer has some kind of media to store data. Personal computers use hard disks to store operating system, software and other user files. To transfer files to other computers we also use USB flash disks or other type of external storage. We expect that everything we save will also stay there forever. We take this for granted without thinking how the data is actually saved.
The fact is that every storage device uses some physical property or process to store data. Since nothing lasts forever sooner or later our storage device will fail. The failure may not be complete, it may happen that only few bits were not saved as they should be. In most cases such small deviations are not problematic. Most storage devices use some kind of error detection and correction. For hard disks it is normal that some sectors fail to store data properly. Therefore there are many algorithms and protection mechanisms that take automatically care for such failures.
Another measure that is used to prevent loss of important data is to create regular backups. The data is simply copied to another media, usually stored in a different location. So if the primary media fails you still have data somewhere else. Of course, making backups increases the cost of storing data, but usually the cost of losing all the saved data is much higher so investment in a reliable backup system always makes sense.
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